title: Alternative TFAP2A isoforms have distinct activities in breast cancer.
abstract: BACKGROUND
  AP-2α is a transcription factor implicated in the regulation of differentiation and proliferation in certain tissues, including the mammary gland. In breast tumours, continued expression of AP-2α has been correlated with a better prognosis, but this is hard to reconcile with a reported role in the upregulation of the ERBB2 oncogene. The existence of TFAP2A isoforms, deriving from alternative first exons and differing in their N-terminal sequence, has been described in some mammals, but their relative abundance and activity has not been investigated in the human breast.
  
  
  METHODS
  Expression levels of four TFAP2A isoforms were assayed at the level of RNA and protein (via the generation of isoform-specific antibodies) in a panel of breast tumour cell lines and in tissue from normal breast and primary tumour samples. Expression constructs for each isoform were used in reporter assays with synthetic and natural promoters (cyclin D3 and ERBB2) to compare the activation and repression activity of the isoforms.
  
  
  RESULTS
  We demonstrate that the two isoforms AP-2α 1b and AP-2α 1c, in addition to the originally cloned, AP-2α 1a, are conserved throughout evolution in vertebrates. Moreover, we show that isoform 1c in particular is expressed at levels at least on a par with the 1a isoform in breast epithelial lines and tissues and may be more highly expressed in tamoxifen resistant tumours. The isoforms share a similar transactivation mechanism involving the recruitment of the adaptors CITED2 or 4 and the transactivators p300 or CBP. However, isoform 1b and 1c are stronger transactivators of the ERBB2 promoter than isoform 1a. In contrast, AP-2α 1a is the only isoform able to act as a repressor, an activity that requires an intact sumoylation motif present within the N-terminus of the protein, and which the other two isoforms lack.
  
  
  CONCLUSIONS
  Our findings suggest that TFAP2A isoforms may be differentially regulated during breast tumourigenesis and this, coupled with differences in their transcriptional activity, may impact on tumour responses to tamoxifen therapy. These data also have implications for the interpretation of tumour studies that seek to correlate outcomes with TFAP2A expression level.
authors.affiliation: Centre for Tumour Biology, Bart's Cancer Institute, Queen Mary University of London, Charterhouse Square, London EC1M 6BQ, UK.
authors.forename: Chiara
authors.initials: C
authors.lastname: Berlato
authors.forename: KaYi V
authors.initials: KV
authors.lastname: Chan
authors.forename: Anna M
authors.initials: AM
authors.lastname: Price
authors.forename: Monica
authors.initials: M
authors.lastname: Canosa
authors.forename: Angelo G
authors.initials: AG
authors.lastname: Scibetta
authors.forename: Helen C
authors.initials: HC
authors.lastname: Hurst
mesh_terms: D000818:Animals; D000911:Antibodies, Monoclonal / Q000276:immunology; D001943:Breast Neoplasms / Q000235:genetics* / Q000378:metabolism; D045744:Cell Line, Tumor; D056743:Cyclin D3 / Q000235:genetics; D019008:Drug Resistance, Neoplasm; D005260:Female; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D011401:Promoter Regions, Genetic; D020033:Protein Isoforms / Q000276:immunology / Q000378:metabolism; D012333:RNA, Messenger / Q000096:biosynthesis / Q000235:genetics; D018719:Erb-b2 Receptor Tyrosine Kinases / Q000235:genetics; D025841:Small Ubiquitin-Related Modifier Proteins / Q000378:metabolism; D013629:Tamoxifen / Q000627:therapeutic use; D050656:Transcription Factor AP-2 / Q000235:genetics* / Q000276:immunology / Q000378:metabolism*; D014158:Transcription, Genetic; D015533:Transcriptional Activation; D014981:Xenopus; D029867:Xenopus Proteins / Q000235:genetics; D015027:Zebrafish; D029961:Zebrafish Proteins / Q000235:genetics
chemical_list: D000911:Antibodies, Monoclonal; D056743:Cyclin D3; D020033:Protein Isoforms; D012333:RNA, Messenger; D018719:Erb-b2 Receptor Tyrosine Kinases; D025841:Small Ubiquitin-Related Modifier Proteins; D013629:Tamoxifen; D050656:Transcription Factor AP-2; D029867:Xenopus Proteins; D029961:Zebrafish Proteins; C493673:TFAP2A protein, human; C508053:ERBB2 protein, human